From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758524AbaDVVIK (ORCPT ); Tue, 22 Apr 2014 17:08:10 -0400 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:53853 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758080AbaDVVIF (ORCPT ); Tue, 22 Apr 2014 17:08:05 -0400 Message-ID: <5356DA2F.8080606@de.ibm.com> Date: Tue, 22 Apr 2014 23:07:59 +0200 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Oleg Nesterov , Avi Kivity , Gleb Natapov , Paolo Bonzini CC: Dominik Dingel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute() References: <20140421132558.GA13608@redhat.com> <5356CDDF.5000203@de.ibm.com> In-Reply-To: <5356CDDF.5000203@de.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14042221-3548-0000-0000-000008D2140F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/04/14 22:15, Christian Borntraeger wrote: > On 21/04/14 15:25, Oleg Nesterov wrote: >> async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) >> should work just fine even if current has another or NULL ->mm. >> >> Recently kvm_async_page_present_sync() was added insedie the "use_mm" >> section, but it seems that it doesn't need current->mm too. >> >> Signed-off-by: Oleg Nesterov > > Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. > This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present > might call apf_put_user which might call copy_to_user, so this is not ok, I guess. wanted to say kvm_arch_async_page_not_present, but I have to correct myself. x86 does the "page is there" in the cpu loop, not in the worker. The cpu look d oes have a valid mm. So this patch should be also ok. > >> --- >> virt/kvm/async_pf.c | 2 -- >> 1 files changed, 0 insertions(+), 2 deletions(-) >> >> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c >> index 10df100..0ced4f3 100644 >> --- a/virt/kvm/async_pf.c >> +++ b/virt/kvm/async_pf.c >> @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) >> >> might_sleep(); >> >> - use_mm(mm); >> down_read(&mm->mmap_sem); >> get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); >> up_read(&mm->mmap_sem); >> kvm_async_page_present_sync(vcpu, apf); >> - unuse_mm(mm); >> >> spin_lock(&vcpu->async_pf.lock); >> list_add_tail(&apf->link, &vcpu->async_pf.done); >> > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >